Hippocampal and cortical primary cilia are required for aversive memory in mice

Temporal Ablation of the Ciliary Protein IFT88 Alters Normal Brainwave Patterns

The primary cilium is a hair-like organelle that hosts molecular machinery for various developmental and homeostatic signaling pathways. Its alteration can cause rare ciliopathies such as the Bardet-Biedl and Joubert syndromes, but is also linked to Alzheimer's disease, clinical depression, and autism spectrum disorder. These afflictions are caused by disturbances in a wide variety of genes but a common phenotype amongst them is cognitive impairment. While cilia-mediated neural function has been widely examined in early neurodevelopment, their function in the adult brain is not well understood. To help elucidate the role of cilia in neural activity, we temporally induced the ablation of IFT88, a gene encoding the intraflagellar transport 88 protein which is neccessary for ciliogenesis, in adult mice before performing memory-related behavioral assays and electroencephalogram/electromyogram (EEG/EMG) recordings. Inducible IFT88 KO mice exhibited severe learning deficits in trace fear conditioning and Morris water maze tests. They had strongly affected brainwave activity both under isoflurane induced anesthesia and during normal activity. And additionally, inducible IFT88 KO mice had altered sleep architecture and attenuated phase-amplitude coupling, a process that underlies learning and memory formation. These results highlight the growing significance of primary cilia for healthy neural function in the adult brain.

The Nociceptor Primary Cilium Contributes to Mechanical Nociceptive Threshold and Inflammatory and Neuropathic Pain

The primary cilium, a single microtubule-based organelle protruding from the cell surface and critical for neural development, also functions in adult neurons. While some dorsal root ganglion neurons elaborate a primary cilium, whether it is expressed by and functional in nociceptors is unknown. Recent studies have shown the role of Hedgehog, whose canonical signaling is primary cilium dependent, in nociceptor sensitization. We establish the presence of primary cilia in soma of rat nociceptors, where they contribute to mechanical threshold, prostaglandin E2 (PGE2)-induced hyperalgesia, and chemotherapy-induced neuropathic pain (CIPN). Intrathecal administration of siRNA targeting Ift88, a primary cilium-specific intraflagellar transport (IFT) protein required for ciliary integrity, resulted in attenuation of Ift88 mRNA and nociceptor primary cilia. Attenuation of primary cilia was associated with an increase in mechanical nociceptive threshold in vivo and decrease in nociceptor excitability in vitro, abrogation of hyperalgesia, and nociceptor sensitization induced by both a prototypical pronociceptive inflammatory mediator PGE2 and paclitaxel CIPN, in a sex-specific fashion. siRNA targeting Ift52, another IFT protein, and knockdown of NompB, the Drosophila Ift88 ortholog, also abrogated CIPN and reduced baseline mechanosensitivity, respectively, providing independent confirmation for primary cilia control of nociceptor function. Hedgehog-induced hyperalgesia is attenuated by Ift88 siRNA, supporting the role for primary cilia in Hedgehog-induced hyperalgesia. Attenuation of CIPN by cyclopamine (intradermal and intraganglion), which inhibits Hedgehog signaling, supports the role of Hedgehog in CIPN. Our findings support the role of the nociceptor primary cilium in control of mechanical nociceptive threshold and inflammatory and neuropathic pain, the latter Hedgehog-dependent.

The Primary Cilium and its Hedgehog Signaling in Nociceptors Contribute to Inflammatory and Neuropathic Pain

The primary cilium, a 1-3 μm long hair-like structure protruding from the surface of almost all cells in the vertebrate body, is critical for neuronal development and also functions in the adult. As the migratory neural crest settles into dorsal root ganglia (DRG) sensory neurons elaborate a single primary cilium at their soma that is maintained into adult stages. While it is not known if primary cilia are expressed in nociceptors, or their potential function in the mature DRG neuron, recent studies have shown a role for Hedgehog, whose signaling demonstrates a dependence on primary cilia, in nociceptor sensitization. Here we report the expression of primary cilia in rat and mouse nociceptors, where they modulate mechanical nociceptive threshold, and contribute to inflammatory and neuropathic pain. When siRNA targeting Ift88, a primary cilium-specific intraflagellar transport (IFT) protein required for ciliary integrity, was administered by intrathecal injection, in the rat, it resulted in loss of Ift88 mRNA in DRG, and primary cilia in neuronal cell bodies, which was associated with an increase in mechanical nociceptive threshold, and abrogation of hyperalgesia induced by the pronociceptive inflammatory mediator, prostaglandin E2, and painful peripheral neuropathy induced by a neurotoxic chemotherapy drug, paclitaxel. To provide further support for the role of the primary cilium in nociceptor function we also administered siRNA for another IFT protein, Ift52. Ift52 siRNA results in loss of Ift52 in DRG and abrogates paclitaxel-induced painful peripheral neuropathy. Attenuation of Hedgehog-induced hyperalgesia by Ift88 knockdown supports a role for the primary cilium in the hyperalgesia induced by Hedgehog, and attenuation of paclitaxel chemotherapy-induced neuropathy (CIPN) by cyclopamine, which attenuates Hedgehog signaling, suggests a role of Hedgehog in CIPN. Our findings support a role of nociceptor primary cilia in the control of mechanical nociceptive threshold and in inflammatory and neuropathic pain, the latter, at least in part, Hedgehog dependent.

Cilia Provide a Platform for the Generation, Regulated Secretion, and Reception of Peptidergic Signals

Cilia are microtubule-based cellular projections that act as motile, sensory, and secretory organelles. These structures receive information from the environment and transmit downstream signals to the cell body. Cilia also release vesicular ectosomes that bud from the ciliary membrane and carry an array of bioactive enzymes and peptide products. Peptidergic signals represent an ancient mode of intercellular communication, and in metazoans are involved in the maintenance of cellular homeostasis and various other physiological processes and responses. Numerous peptide receptors, subtilisin-like proteases, the peptide-amidating enzyme, and bioactive amidated peptide products have been localized to these organelles. In this review, we detail how cilia serve as specialized signaling organelles and act as a platform for the regulated processing and secretion of peptidergic signals. We especially focus on the processing and trafficking pathways by which a peptide precursor from the green alga Chlamydomonas reinhardtii is converted into an amidated bioactive product-a chemotactic modulator-and released from cilia in ectosomes. Biochemical dissection of this complex ciliary secretory pathway provides a paradigm for understanding cilia-based peptidergic signaling in mammals and other eukaryotes.

Role of lipids in the control of autophagy and primary cilium signaling in neurons

The brain is, after the adipose tissue, the organ with the greatest amount of lipids and diversity in their composition in the human body. In neurons, lipids are involved in signaling pathways controlling autophagy, a lysosome-dependent catabolic process essential for the maintenance of neuronal homeostasis and the function of the primary cilium, a cellular antenna that acts as a communication hub that transfers extracellular signals into intracellular responses required for neurogenesis and brain development. A crosstalk between primary cilia and autophagy has been established; however, its role in the control of neuronal activity and homeostasis is barely known. In this review, we briefly discuss the current knowledge regarding the role of autophagy and the primary cilium in neurons. Then we review the recent literature about specific lipid subclasses in the regulation of autophagy, in the control of primary cilium structure and its dependent cellular signaling in physiological and pathological conditions, specifically focusing on neurons, an area of research that could have major implications in neurodevelopment, energy homeostasis, and neurodegeneration.

Cilia loss on distinct neuron populations differentially alters cocaine-induced locomotion and reward

BACKGROUND

Neuronal primary cilia are being recognized for their role in mediating signaling associated with a variety of neurobehaviors, including responses to drugs of abuse. They function as signaling hubs, enriched with a diverse array of G-protein coupled receptors (GPCRs), including several associated with motivation and drug-related behaviors. However, our understanding of how cilia regulate neuronal function and behavior is still limited.

AIMS

The objective of the current study was to investigate the contributions of primary cilia on specific neuronal populations to behavioral responses to cocaine.

METHODS

To test the consequences of cilia loss on cocaine-induced locomotion and reward-related behavior, we selectively ablated cilia from dopaminergic or GAD2-GABAergic neurons in mice.

RESULTS

Cilia ablation on either population of neurons failed to significantly alter acute locomotor responses to cocaine at a range of doses. With repeated administration, mice lacking cilia on GAD2-GABAergic neurons showed no difference in locomotor sensitization to cocaine compared to wild-type (WT) littermates, whereas mice lacking cilia on dopaminergic neurons exhibited reduced locomotor sensitization to cocaine at 10 and 30 mg/kg. Mice lacking cilia on GAD2-GABAergic neurons showed no difference in cocaine conditioned place preference (CPP), whereas mice lacking cilia on dopaminergic neurons exhibited reduced CPP compared to WT littermates.

CONCLUSIONS

Combined with previous findings using amphetamine, our results show that behavioral effects of cilia ablation are cell- and drug type-specific, and that neuronal cilia contribute to modulation of both the locomotor-inducing and rewarding properties of cocaine.

Biomarkers in Alzheimer's Disease: Are Olfactory Neuronal Precursors Useful for Antemortem Biomarker Research?

Alzheimer's disease (AD), as the main cause of dementia, affects millions of people around the world, whose diagnosis is based mainly on clinical criteria. Unfortunately, the diagnosis is obtained very late, when the neurodegenerative damage is significant for most patients. Therefore, the exhaustive study of biomarkers is indispensable for diagnostic, prognostic, and even follow-up support. AD is a multifactorial disease, and knowing its underlying pathological mechanisms is crucial to propose new and valuable biomarkers. In this review, we summarize some of the main biomarkers described in AD, which have been evaluated mainly by imaging studies in cerebrospinal fluid and blood samples. Furthermore, we describe and propose neuronal precursors derived from the olfactory neuroepithelium as a potential resource to evaluate some of the widely known biomarkers of AD and to gear toward searching for new biomarkers. These neuronal lineage cells, which can be obtained directly from patients through a non-invasive and outpatient procedure, display several characteristics that validate them as a surrogate model to study the central nervous system, allowing the analysis of AD pathophysiological processes. Moreover, the ease of obtaining and harvesting endows them as an accessible and powerful resource to evaluate biomarkers in clinical practice.

The Primary Cilium and its Hedgehog Signaling in Nociceptors Contribute to Inflammatory and Neuropathic Pain

The primary cilium, a 1-3 μm long hair-like structure protruding from the surface of almost all cells in the vertebrate body, is critical for neuronal development and also functions in the adult. As the migratory neural crest settles into dorsal root ganglia (DRG) sensory neurons elaborate a single primary cilium at their soma that is maintained into adult stages. While it is not known if primary cilia are expressed in nociceptors, or their potential function in the mature DRG neuron, recent studies have shown a role for Hedgehog, whose signaling demonstrates a dependence on primary cilia, in nociceptor sensitization. Here we report the expression of primary cilia in rat and mouse nociceptors, where they modulate mechanical nociceptive threshold, and contribute to inflammatory and neuropathic pain. When siRNA targeting Ift88 , a primary cilium-specific intra-flagellar transport (IFT) protein required for ciliary integrity, was administered by intrathecal injection, in the rat, it resulted in loss of Ift88 mRNA in DRG, and primary cilia in neuronal cell bodies, which was associated with an increase in mechanical nociceptive threshold, and abrogation of hyperalgesia induced by the pronociceptive inflammatory mediator, prostaglandin E 2 , and painful peripheral neuropathy induced by a neurotoxic chemotherapy drug, paclitaxel. To provide further support for the role of the primary cilium in nociceptor function we also administered siRNA for another IFT protein, Ift 52. Ift 52 siRNA results in loss of Ift 52 in DRG and abrogates paclitaxel-induced painful peripheral neuropathy. Attenuation of Hedgehog-induced hyperalgesia by Ift88 knockdown supports a role for the primary cilium in the hyperalgesia induced by Hedgehog, and attenuation of paclitaxel chemotherapy-induced neuropathy (CIPN) by cyclopamine, which attenuates Hedgehog signaling, suggests a role of Hedgehog in CIPN. Our findings support a role of nociceptor primary cilia in the control of mechanical nociceptive threshold and in inflammatory and neuropathic pain, the latter, at least in part, Hedgehog dependent.

MATS: a novel multi-ancestry transcriptome-wide association study to account for heterogeneity in the effects of cis-regulated gene expression on complex traits

The Transcriptome-Wide Association Study (TWAS) is a widely used approach which integrates gene expression and Genome Wide Association Study (GWAS) data to study the role of cis-regulated gene expression (GEx) in complex traits. However, the genetic architecture of GEx varies across populations, and recent findings point to possible ancestral heterogeneity in the effects of GEx on complex traits, which may be amplified in TWAS by modeling GEx as a function of cis-eQTLs. Here, we present a novel extension to TWAS to account for heterogeneity in the effects of cis-regulated GEx which are correlated with ancestry. Our proposed Multi-Ancestry TwaS (MATS) framework jointly analyzes samples from multiple populations and distinguishes between shared, ancestry-specific and/or subject-specific expression-trait associations. As such, MATS amplifies power to detect shared GEx associations over ancestry-stratified TWAS through increased sample sizes, and facilitates the detection of genes with subgroup-specific associations which may be masked by standard TWAS. Our simulations highlight the improved Type-I error conservation and power of MATS compared with competing approaches. Our real data applications to Alzheimer's disease (AD) case-control genotypes from the Alzheimer's Disease Sequencing Project (ADSP) and continuous phenotypes from the UK Biobank (UKBB) identify a number of unique gene-trait associations which were not discovered through standard and/or ancestry-stratified TWAS. Ultimately, these findings promote MATS as a powerful method for detecting and estimating significant gene expression effects on complex traits within multi-ancestry cohorts and corroborates the mounting evidence for inter-population heterogeneity in gene-trait associations.

Caspase-3 Inhibition toward Perinatal Protection of the Developing Brain from Environmental Stress

Throughout our lives, we are exposed to a variety of hazards, such as environmental pollutants and chemical substances that affect our health, and viruses and bacteria that cause infectious diseases. These external factors that are undesirable to an organism are called environmental stress. During the perinatal period, when neural networks are drastically reorganized and refined, the tolerance of the developing brain to various environmental stresses is lower than in adulthood. Thus, exposure to environmental stress during this vulnerable period is strongly associated with cognitive and behavioral deficits in later life. Recent studies have uncovered various mechanisms underlying the adverse impacts of environmental stress during the perinatal period on brain development. In this mini-review, we will present the findings from these studies, focusing on caspase-mediated apoptotic and nonapoptotic effects of environmental stress, and discuss several compounds that mitigate these caspase-mediated effects as examples of potential therapeutic approaches.

Myristoylated Neuronal Calcium Sensor-1 captures the ciliary vesicle at distal appendages

The primary cilium is a microtubule-based organelle that cycles through assembly and disassembly. In many cell types, formation of the cilium is initiated by recruitment of ciliary vesicles to the distal appendage of the mother centriole. However, the distal appendage mechanism that directly captures ciliary vesicles is yet to be identified. In an accompanying paper, we show that the distal appendage protein, CEP89, is important for thef ciliary vesicle recruitment, but not for other steps of cilium formation (Tomoharu Kanie, Love, Fisher, Gustavsson, & Jackson, 2023). The lack of a membrane binding motif in CEP89 suggests that it may indirectly recruit ciliary vesicles via another binding partner. Here, we identify Neuronal Calcium Sensor-1 (NCS1) as a stoichiometric interactor of CEP89. NCS1 localizes to the position between CEP89 and a ciliary vesicle marker, RAB34, at the distal appendage. This localization was completely abolished in CEP89 knockouts, suggesting that CEP89 recruits NCS1 to the distal appendage. Similarly to CEP89 knockouts, ciliary vesicle recruitment as well as subsequent cilium formation was perturbed in NCS1 knockout cells. The ability of NCS1 to recruit the ciliary vesicle is dependent on its myristoylation motif and NCS1 knockout cells expressing myristoylation defective mutant failed to rescue the vesicle recruitment defect despite localizing proper localization to the centriole. In sum, our analysis reveals the first known mechanism for how the distal appendage recruits the ciliary vesicles.

Cilia in the Striatum Mediate Timing-Dependent Functions

Almost all brain cells contain cilia, antennae-like microtubule-based organelles. Yet, the significance of cilia, once considered vestigial organelles, in the higher-order brain functions is unknown. Cilia act as a hub that senses and transduces environmental sensory stimuli to generate an appropriate cellular response. Similarly, the striatum, a brain structure enriched in cilia, functions as a hub that receives and integrates various types of environmental information to drive appropriate motor response. To understand cilia's role in the striatum functions, we used loxP/Cre technology to ablate cilia from the dorsal striatum of male mice and monitored the behavioral consequences. Our results revealed an essential role for striatal cilia in the acquisition and brief storage of information, including learning new motor skills, but not in long-term consolidation of information or maintaining habitual/learned motor skills. A fundamental aspect of all disrupted functions was the "time perception/judgment deficit." Furthermore, the observed behavioral deficits form a cluster pertaining to clinical manifestations overlapping across psychiatric disorders that involve the striatum functions and are known to exhibit timing deficits. Thus, striatal cilia may act as a calibrator of the timing functions of the basal ganglia-cortical circuit by maintaining proper timing perception. Our findings suggest that dysfunctional cilia may contribute to the pathophysiology of neuro-psychiatric disorders, as related to deficits in timing perception.

Oligodendroglial primary cilium heterogeneity during development and demyelination/remyelination

The primary cilium (PC) has emerged as an indispensable cellular antenna essential for signal transduction of important cell signaling pathways. The rapid acquisition of knowledge about PC biology has raised attention to PC as a therapeutic target in some neurological and psychiatric diseases. However, the role of PC in oligodendrocytes and its participation in myelination/remyelination remain poorly understood. Oligodendrocyte precursor cells (OPCs) give rise to oligodendrocytes during central nervous system (CNS) development. In adult, a small percentage of OPCs remains as undifferentiated cells located sparsely in the different regions of the CNS. These cells can regenerate oligodendrocytes and participate to certain extent in remyelination. This study aims characterize PC in oligodendrocyte lineage cells during post-natal development and in a mouse model of demyelination/remyelination. We show heterogeneity in the frequency of cilium presence on OPCs, depending on culture conditions in vitro and cerebral regions in vivo during development and demyelination/remyelination. In vitro, Lithium chloride (LiCl), Forskolin and Chloral Hydrate differentially affect cilium, depending on culture environment and PC length correlates with the cell differentiation state. Beside the role of PC as a keeper of cell proliferation, our results suggest its involvement in myelination/remyelination.

Large-scale analysis reveals spatiotemporal circadian patterns of cilia transcriptomes in the primate brain

Cilia are dynamic subcellular systems, with core structural and functional components operating in a highly coordinated manner. Since many environmental stimuli sensed by cilia are circadian in nature, it is reasonable to speculate that genes encoding cilia structural and functional components follow rhythmic circadian patterns of expression. Using computational methods and the largest spatiotemporal gene expression atlas of primates, we identified and analyzed the circadian rhythmic expression of cilia genes across 22 primate brain areas. We found that around 73% of cilia transcripts exhibited circadian rhythmicity across at least one of 22 brain regions. In 12 brain regions, cilia transcriptomes were significantly enriched with circadian oscillating transcripts, as compared to the rest of the transcriptome. The phase of the cilia circadian transcripts deviated from the phase of the majority of the background circadian transcripts, and transcripts coding for cilia basal body components accounted for the majority of cilia circadian transcripts. In addition, adjacent or functionally connected brain nuclei had large overlapping complements of circadian cilia genes. Most remarkably, cilia circadian transcripts shared across the basal ganglia nuclei and the prefrontal cortex peaked in these structures in sequential fashion that is similar to the sequential order of activation of the basal ganglia-cortical circuitry in connection with movement coordination, albeit on completely different timescales. These findings support a role for the circadian spatiotemporal orchestration of cilia gene expression in the normal physiology of the basal ganglia-cortical circuit and motor control. Studying orchestrated cilia rhythmicity in the basal ganglia-cortical circuits and other brain circuits may help develop better functional models, and shed light on the causal effects cilia functions have on these circuits and on the regulation of movement and other behaviors.

Primary cilia are required for the persistence of memory and stabilization of perineuronal nets

It is well established that the formation of episodic memories requires multiple hippocampal mechanisms operating on different time scales. Early mechanisms of memory formation (synaptic consolidation) have been extensively characterized. However, delayed mechanisms, which maintain hippocampal activity as memories stabilize in cortical circuits, are not well understood. Here we demonstrate that contrary to the transient expression of early- and delayed-response genes, the expression of cytoskeleton- and extracellular matrix-associated genes remains dynamic even at remote time points. The most profound expression changes clustered around primary cilium-associated and collagen genes. These genes most likely contribute to memory by stabilizing perineuronal nets in the dorsohippocampal CA1 subfield, as revealed by targeted disruptions of the primary cilium or perineuronal nets. The findings show that nonsynaptic, primary cilium-mediated mechanisms are required for the persistence of context memory.

An N-terminal fusion allele to study melanin concentrating hormone receptor 1

Cilia on neurons play critical roles in both the development and function of the central nervous system (CNS). While it remains challenging to elucidate the precise roles for neuronal cilia, it is clear that a subset of G-protein-coupled receptors (GPCRs) preferentially localize to the cilia membrane. Further, ciliary GPCR signaling has been implicated in regulating a variety of behaviors. Melanin concentrating hormone receptor 1 (MCHR1), is a GPCR expressed centrally in rodents known to be enriched in cilia. Here we have used MCHR1 as a model ciliary GPCR to develop a strategy to fluorescently tag receptors expressed from the endogenous locus in vivo. Using CRISPR/Cas9, we inserted the coding sequence of the fluorescent protein mCherry into the N-terminus of Mchr1. Analysis of the fusion protein (^mCherry MCHR1) revealed its localization to neuronal cilia in the CNS, across multiple developmental time points and in various regions of the adult brain. Our approach simultaneously produced fortuitous in/dels altering the Mchr1 start codon resulting in a new MCHR1 knockout line. Functional studies using electrophysiology show a significant alteration of synaptic strength in MCHR1 knockout mice. A reduction in strength is also detected in mice homozygous for the mCherry insertion, suggesting that while the strategy is useful for monitoring the receptor, activity could be altered. However, both lines should aid in studies of MCHR1 function and contribute to our understanding of MCHR1 signaling in the brain. Additionally, this approach could be expanded to aid in the study of other ciliary GPCRs.

A mouse model of Bardet-Biedl Syndrome has impaired fear memory, which is rescued by lithium treatment

Primary cilia are microtubule-based organelles present on most cells that regulate many physiological processes, ranging from maintaining energy homeostasis to renal function. However, the role of these structures in the regulation of behavior remains unknown. To study the role of cilia in behavior, we employ mouse models of the human ciliopathy, Bardet-Biedl Syndrome (BBS). Here, we demonstrate that BBS mice have significant impairments in context fear conditioning, a form of associative learning. Moreover, we show that postnatal deletion of BBS gene function, as well as congenital deletion, specifically in the forebrain, impairs context fear conditioning. Analyses indicated that these behavioral impairments are not the result of impaired hippocampal long-term potentiation. However, our results indicate that these behavioral impairments are the result of impaired hippocampal neurogenesis. Two-week treatment with lithium chloride partially restores the proliferation of hippocampal neurons which leads to a rescue of context fear conditioning. Overall, our results identify a novel role of cilia genes in hippocampal neurogenesis and long-term context fear conditioning.

Ciliary neuropeptidergic signaling dynamically regulates excitatory synapses in postnatal neocortical pyramidal neurons

Primary cilia are compartmentalized sensory organelles present on the majority of neurons in the mammalian brain throughout adulthood. Recent evidence suggests that cilia regulate multiple aspects of neuronal development, including the maintenance of neuronal connectivity. However, whether ciliary signals can dynamically modulate postnatal circuit excitability is unknown. Here we show that acute cell-autonomous knockdown of ciliary signaling rapidly strengthens glutamatergic inputs onto cultured rat neocortical pyramidal neurons and increases spontaneous firing. This increased excitability occurs without changes to passive neuronal properties or intrinsic excitability. Further, the neuropeptide receptor somatostatin receptor 3 (SSTR3) is localized nearly exclusively to excitatory neuron cilia both in vivo and in culture, and pharmacological manipulation of SSTR3 signaling bidirectionally modulates excitatory synaptic inputs onto these neurons. Our results indicate that ciliary neuropeptidergic signaling dynamically modulates excitatory synapses and suggest that defects in this regulation may underlie a subset of behavioral and cognitive disorders associated with ciliopathies.

Behavioral Tasks Evaluating Schizophrenia-like Symptoms in Animal Models: A Recent Update

BACKGROUND

Schizophrenia is a serious mental illness that affects more than 21 million people worldwide. Both genetics and the environment play a role in its etiology and pathogenesis. Symptoms of schizophrenia are mainly categorized into positive, negative, and cognitive. One major approach to identify and understand these diverse symptoms in humans has been to study behavioral phenotypes in a range of animal models of schizophrenia.

OBJECTIVE

We aimed to provide a comprehensive review of the behavioral tasks commonly used for measuring schizophrenia-like behaviors in rodents together with an update of the recent study findings.

METHODS

Articles describing phenotypes of schizophrenia-like behaviors in various animal models were collected through a literature search in Google Scholar, PubMed, Web of Science, and Scopus, with a focus on advances over the last 10 years.

RESULTS

Numerous studies have used a range of animal models and behavioral paradigms of schizophrenia to develop antipsychotic drugs for improved therapeutics. In establishing animal models of schizophrenia, the candidate models were evaluated for schizophrenia-like behaviors using several behavioral tasks for positive, negative, and cognitive symptoms designed to verify human symptoms of schizophrenia. Such validated animal models were provided as rapid preclinical avenues for drug testing and mechanistic studies.

CONCLUSION

Based on the most recent advances in the field, it is apparent that a myriad of behavior tests are needed to confirm and evaluate the congruency of animal models with the numerous behaviors and clinical signs exhibited by patients with schizophrenia.

Primary cilia safeguard cortical neurons in neonatal mouse forebrain from environmental stress-induced dendritic degeneration

The developing brain is under the risk of exposure to a multitude of environmental stressors. While perinatal exposure to excessive levels of environmental stress is responsible for a wide spectrum of neurological and psychiatric conditions, the developing brain is equipped with intrinsic cell protection, the mechanisms of which remain unknown. Here we show, using neonatal mouse as a model system, that primary cilia, hair-like protrusions from the neuronal cell body, play an essential role in protecting immature neurons from the negative impacts of exposure to environmental stress. More specifically, we found that primary cilia prevent the degeneration of dendritic arbors upon exposure to alcohol and ketamine, two major cell stressors, by activating cilia-localized insulin-like growth factor 1 receptor and downstream Akt signaling. We also found that activation of this pathway inhibits Caspase-3 activation and caspase-mediated cleavage/fragmentation of cytoskeletal proteins in stress-exposed neurons. These results indicate that primary cilia play an integral role in mitigating adverse impacts of environmental stressors such as drugs on perinatal brain development.

Properties of primary cilia in melanin-concentrating hormone receptor 1-bearing hippocampal neurons in vivo and in vitro

The primary cilium is a solitary organelle that organizes a sensitive signaling hub in a highly ordered microenvironment. Cilia are plastic structures, changing their length in response to bioactive substances, and ciliary length may be regulated to ensure efficient signaling capacity. Mammalian brain neurons possess primary cilia that are enriched in a set of G protein-coupled receptors (GPCRs), including the feeding-related melanin-concentrating hormone (MCH) receptor 1 (MCHR1). We previously demonstrated a novel biological phenomenon, ciliary MCHR1-mediated cilia length shortening through Gi/o and Akt signaling, using a simple cell culture model of human retinal pigmented epithelial RPE1 cells exogenously expressing MCHR1. In the present study, we characterized the properties of endogenous MCHR1-expressing primary cilia in hippocampal neurons in rodents. Using cultured dissociated rat hippocampal neurons in vitro, we showed that MCH triggered cilia length reduction involved in MCHR1-Gi/o and -Akt signaling. In rat hippocampal slice cultures with preservation of the cytoarchitecture and cell populations, ciliary MCHR1 was abundantly located in the CA1 and CA3 regions, but not in the dentate gyrus. Notably, treatment of slice cultures with MCH induced Gi/o- and Akt-dependent cilia shortening in the CA1 region without influencing cilia length in the CA3 region. Regarding the in vivo mouse brain, we observed higher levels of ciliary MCHR1 in the CA1 and CA3 regions as well as in slice cultures. In the starved state mice, a marked increase in MCH mRNA expression was detected in the lateral hypothalamus. Furthermore, MCHR1-positive cilia length in the hippocampal CA1 region was significantly shortened in fasted mice compared with fed mice. The present findings focused on the hippocampus provide a potential approach to investigate how MCHR1-driven cilia shortening regulates neuronal activity and physiological function toward feeding and memory tasks.

Neuron-specific cilia loss differentially alters locomotor responses to amphetamine in mice

The neural mechanisms that underlie responses to drugs of abuse are complex, and impacted by a number of neuromodulatory peptides. Within the past 10 years it has been discovered that several of the receptors for neuromodulators are enriched in the primary cilia of neurons. Primary cilia are microtubule-based organelles that project from the surface of nearly all mammalian cells, including neurons. Despite what we know about cilia, our understanding of how cilia regulate neuronal function and behavior is still limited. The primary objective of this study was to investigate the contributions of primary cilia on specific neuronal populations to behavioral responses to amphetamine. To test the consequences of cilia loss on amphetamine-induced locomotor activity we selectively ablated cilia from dopaminergic or GAD2-GABAergic neurons in mice. Cilia loss had no effect on baseline locomotion in either mouse strain. In mice lacking cilia on dopaminergic neurons, locomotor activity compared to wild- type mice was reduced in both sexes in response to acute administration of 3.0 mg/kg amphetamine. In contrast, changes in the locomotor response to amphetamine in mice lacking cilia on GAD2-GABAergic neurons were primarily driven by reductions in locomotor activity in males. Following repeated amphetamine administration (1.0 mg kg^-1  day^-1 over 5 days), mice lacking cilia on GAD2-GABAergic neurons exhibited enhanced sensitization of the locomotor stimulant response to the drug, whereas mice lacking cilia on dopaminergic neurons did not differ from wild-type controls. These results indicate that cilia play neuron-specific roles in both acute and neuroplastic responses to psychostimulant drugs of abuse.

Transcriptional Profiling of Primate Central Nucleus of the Amygdala Neurons to Understand the Molecular Underpinnings of Early-Life Anxious Temperament

BACKGROUND

Children exhibiting extreme anxious temperament (AT) are at an increased risk for developing anxiety and depression. Our previous mechanistic and neuroimaging work in young rhesus monkeys linked the central nucleus of the amygdala to AT and its underlying neural circuit.

METHODS

Here, we used laser capture microscopy and RNA sequencing in 47 young rhesus monkeys to investigate AT's molecular underpinnings by focusing on neurons from the lateral division of the central nucleus of the amygdala (CeL). RNA sequencing identified numerous AT-related CeL transcripts, and we used immunofluorescence (n = 3) and tract-tracing (n = 2) methods in a different sample of monkeys to examine the expression, distribution, and projection pattern of neurons expressing one of these transcripts.

RESULTS

We found 555 AT-related transcripts, 14 of which were confirmed with high statistical confidence (false discovery rate < .10), including protein kinase C delta (PKCδ), a CeL microcircuit cell marker implicated in rodent threat processing. We characterized PKCδ neurons in the rhesus CeL, compared its distribution with that of the mouse, and demonstrated that a subset of these neurons project to the laterodorsal bed nucleus of the stria terminalis.

CONCLUSIONS

These findings demonstrate that CeL PKCδ is associated with primate anxiety, provides evidence of a CeL to laterodorsal bed nucleus of the stria terminalis circuit that may be relevant to understanding human anxiety, and points to specific molecules within this circuit that could serve as potential treatment targets for anxiety disorders.

Primary Ciliary Deficits in the Dentate Gyrus of Fragile X Syndrome

The primary cilium is the non-motile cilium present in most mammalian cell types and functions as an antenna for cells to sense signals. Ablating primary cilia in postnatal newborn neurons of the dentate gyrus (DG) results in both reduced dendritic arborization and synaptic strength, leading to hippocampal-dependent learning and memory deficits. Fragile X syndrome (FXS) is a common form of inheritance for intellectual disabilities with a high risk for autism spectrum disorders, and Fmr1 KO mice, a mouse model for FXS, demonstrate deficits in newborn neuron differentiation, dendritic morphology, and memory formation in the DG. Here, we found that the number of primary cilia in Fmr1 KO mice is reduced, specifically in the DG of the hippocampus. Moreover, this cilia loss was observed postnatally mainly in newborn neurons generated from the DG, implicating that these primary ciliary deficits may possibly contribute to the pathophysiology of FXS.

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Primary cilia are significantly reduced in the DG of Fmr1 KO mice

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Fmr1 KO mice show age-dependent primary cilia deficits

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Neuronal ciliogenesis defects are shown in the DG of Fmr1 KO mice

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Primary cilia deficits are observed in newborn neurons from SGZ, but not from DNe

NRF2 and Primary Cilia: An Emerging Partnership

When not dividing, many cell types target their centrosome to the plasma membrane, where it nucleates assembly of a primary cilium, an antenna-like signaling structure consisting of nine concentric microtubule pairs surrounded by membrane. Primary cilia play important pathophysiological roles in many tissues, their dysfunction being associated with cancer and ciliopathies, a diverse group of congenital human diseases. Several recent studies have unveiled functional connections between primary cilia and NRF2 (nuclear factor erythroid 2-related factor 2), the master transcription factor orchestrating cytoprotective responses to oxidative and other cellular stresses. These NRF2-cilia relationships are reciprocal: primary cilia, by promoting autophagy, downregulate NRF2 activity. In turn, NRF2 transcriptionally regulates genes involved in ciliogenesis and Hedgehog (Hh) signaling, a cilia-dependent pathway with major roles in embryogenesis, stem cell function and tumorigenesis. Nevertheless, while we found that NRF2 stimulates ciliogenesis and Hh signaling, a more recent study reported that NRF2 negatively affects these processes. Herein, we review the available evidence linking NRF2 to primary cilia, suggest possible explanations to reconcile seemingly contradictory data, and discuss what the emerging interplay between primary cilia and NRF2 may mean for human health and disease.

TTBK2 and primary cilia are essential for the connectivity and survival of cerebellar Purkinje neurons

Primary cilia are vital signaling organelles that extend from most types of cells, including neurons and glia. These structures are essential for development of many tissues and organs; however, their function in adult tissues, particularly neurons in the brain, remains largely unknown. Tau tubulin kinase 2 (TTBK2) is a critical regulator of ciliogenesis, and is also mutated in a hereditary neurodegenerative disorder, spinocerebellar ataxia type 11 (SCA11). Here, we show that conditional knockout of Ttbk2 in adult mice results in degenerative cerebellar phenotypes that recapitulate aspects of SCA11 including motor coordination deficits and defects to Purkinje cell (PC) integrity. We also find that the Ttbk2 conditional mutant mice quickly lose cilia throughout the brain. We show that conditional knockout of the key ciliary trafficking gene Ift88 in adult mice results in nearly identical cerebellar phenotypes to those of the Ttbk2 knockout, indicating that disruption of ciliary signaling is a key driver of these phenotypes. Our data suggest that primary cilia play an integral role in maintaining the function of PCs in the adult cerebellum and reveal novel insights into mechanisms involved in neurodegeneration.

A neuroscientist's guide to transgenic mice and other genetic tools

The past decade has produced an explosion in the number and variety of genetic tools available to neuroscientists, resulting in an unprecedented ability to precisely manipulate the genome and epigenome in behaving animals. However, no single resource exists that describes all of the tools available to neuroscientists. Here, we review the genetic, transgenic, and viral techniques that are currently available to probe the complex relationship between genes and cognition. Topics covered include types of traditional transgenic mouse models (knockout, knock-in, reporter lines), inducible systems (Cre-loxP, Tet-On, Tet-Off) and cell- and circuit-specific systems (TetTag, TRAP, DIO-DREADD). Additionally, we provide details on virus-mediated and siRNA/shRNA approaches, as well as a comprehensive discussion of the myriad manipulations that can be made using the CRISPR-Cas9 system, including single base pair editing and spatially- and temporally-regulated gene-specific transcriptional control. Collectively, this review will serve as a guide to assist neuroscientists in identifying and choosing the appropriate genetic tools available to study the complex relationship between the brain and behavior.

Cellular signalling by primary cilia in development, organ function and disease

Primary cilia project in a single copy from the surface of most vertebrate cell types; they detect and transmit extracellular cues to regulate diverse cellular processes during development and to maintain tissue homeostasis. The sensory capacity of primary cilia relies on the coordinated trafficking and temporal localization of specific receptors and associated signal transduction modules in the cilium. The canonical Hedgehog (HH) pathway, for example, is a bona fide ciliary signalling system that regulates cell fate and self-renewal in development and tissue homeostasis. Specific receptors and associated signal transduction proteins can also localize to primary cilia in a cell type-dependent manner; available evidence suggests that the ciliary constellation of these proteins can temporally change to allow the cell to adapt to specific developmental and homeostatic cues. Consistent with important roles for primary cilia in signalling, mutations that lead to their dysfunction underlie a pleiotropic group of diseases and syndromic disorders termed ciliopathies, which affect many different tissues and organs of the body. In this Review, we highlight central mechanisms by which primary cilia coordinate HH, G protein-coupled receptor, WNT, receptor tyrosine kinase and transforming growth factor-β (TGFβ)/bone morphogenetic protein (BMP) signalling and illustrate how defects in the balanced output of ciliary signalling events are coupled to developmental disorders and disease progression.

NRF2-dependent gene expression promotes ciliogenesis and Hedgehog signaling

The transcription factor NRF2 is a master regulator of cellular antioxidant and detoxification responses, but it also regulates other processes such as autophagy and pluripotency. In human embryonic stem cells (hESCs), NRF2 antagonizes neuroectoderm differentiation, which only occurs after NRF2 is repressed via a Primary Cilia-Autophagy-NRF2 (PAN) axis. However, the functional connections between NRF2 and primary cilia, microtubule-based plasma membrane protrusions that function as cellular antennae, remain poorly understood. For instance, nothing is known about whether NRF2 affects cilia, or whether cilia regulation of NRF2 extends beyond hESCs. Here, we show that NRF2 and primary cilia reciprocally regulate each other. First, we demonstrate that fibroblasts lacking primary cilia have higher NRF2 activity, which is rescued by autophagy-activating mTOR inhibitors, indicating that the PAN axis also operates in differentiated cells. Furthermore, NRF2 controls cilia formation and function. NRF2-null cells grow fewer and shorter cilia and display impaired Hedgehog signaling, a cilia-dependent pathway. These defects are not due to increased oxidative stress or ciliophagy, but rather to NRF2 promoting expression of multiple ciliogenic and Hedgehog pathway genes. Among these, we focused on GLI2 and GLI3, the transcription factors controlling Hh pathway output. Both their mRNA and protein levels are reduced in NRF2-null cells, consistent with their gene promoters containing consensus ARE sequences predicted to bind NRF2. Moreover, GLI2 and GLI3 fail to accumulate at the ciliary tip of NRF2-null cells upon Hh pathway activation. Given the importance of NRF2 and ciliary signaling in human disease, our data may have important biomedical implications.

A Human Embryonic Stem Cell Model of Aβ-Dependent Chronic Progressive Neurodegeneration

We describe the construction and phenotypic analysis of a human embryonic stem cell model of progressive Aβ-dependent neurodegeneration (ND) with potential relevance to Alzheimer’s disease (AD). We modified one allele of the normal APP locus to directly express a secretory form of Aβ40 or Aβ42, enabling expression from this edited allele to bypass the normal amyloidogenic APP processing pathway. Following neuronal differentiation, edited cell lines specifically accumulate intracellular aggregated/oligomeric Aβ, exhibit a synaptic deficit, and have an abnormal accumulation of endolysosomal vesicles. Edited cultures progress to a stage of overt ND. All phenotypes appear at earlier culture times for Aβ42 relative to Aβ40. Whole transcriptome RNA-Seq analysis identified 23 up and 70 down regulated genes (differentially expressed genes) with similar directional fold change but larger absolute values in the Aβ42 samples suggesting common underlying pathogenic mechanisms. Pathway/annotation analysis suggested that down regulation of extracellular matrix and cilia functions is significantly overrepresented. This cellular model could be useful for uncovering mechanisms directly linking Aβ to neuronal death and as a tool to screen for new therapeutic agents that slow or prevent human ND.

Primary cilium and brain aging: role in neural stem cells, neurodegenerative diseases and glioblastoma

Brain aging is characterized by a progressive loss of tissue integrity and function as a consequence of impaired homeostasis and regeneration capacities. The primary cilium is a highly conserved organelle that projects from the cell surface in a single copy in virtually all mammalian cell types including neural stem/progenitors cells and neurons. Increasing evidence in the last decade points out that primary cilium could be a relevant mediator of neural stem cell activity, neurogenesis, neuronal maturation and maintenance, and brain tumorigenesis. In this review, we summarize the current knowledge about primary cilia roles in these processes. There is currently sufficient background to propose that defective primary cilia contribute to age-related cognitive decline and brain tumor development due to their critical roles in cell cycle control and signaling transduction. This might have potential applications on therapy against age-associated brain diseases.

Neuronal and astrocytic primary cilia in the mature brain

Primary cilia are tiny microtubule-based signaling devices that regulate a variety of physiological functions, including metabolism and cell division. Defects in primary cilia lead to a myriad of diseases in humans such as obesity and cancers. In the mature brain, both neurons and astrocytes contain a single primary cilium. Although neuronal primary cilia are not directly involved in synaptic communication, their pathophysiological impacts on obesity and mental disorders are well recognized. In contrast, research on astrocytic primary cilia lags far behind. Currently, little is known about their functions and molecular pathways in the mature brain. Unlike neurons, postnatal astrocytes retain the capacity of cell division and can become reactive and proliferate in response to various brain insults such as epilepsy, ischemia, traumatic brain injury, and neurodegenerative β-amyloid plaques. Since primary cilia derive from the mother centrioles, astrocyte proliferation must occur in coordination with the dismantling and ciliogenesis of astrocyte cilia. In this regard, the functions, signal pathways, and structural dynamics of neuronal and astrocytic primary cilia are fundamentally different. Here we discuss and compare the current understanding of neuronal and astrocytic primary cilia.

Amyloid-β interrupts canonical Sonic hedgehog signaling by distorting primary cilia structure

Background

Primary cilia are small non-motile microtubule and cell membrane protrusions expressed on most vertebrate cells, including cortical and hippocampal neurons. These small organelles serve as sensory structures sampling the extracellular environment and reprogramming the transcriptional machinery in response to environmental change. Primary cilia are decorated with a variety of receptor proteins and are necessary for specific signaling cascades such as the Sonic hedgehog (Shh) pathway. Disrupting cilia structure or function results in a spectrum of diseases collectively referred to as ciliopathies. Common to human ciliopathies is cognitive impairment, a symptom also observed in Alzheimer's disease (AD). One hallmark of AD is accumulation of senile plaques composed of neurotoxic Amyloid-β (Aβ) peptide. The Aβ peptide is generated by the proteolytic cleavage of the amyloid precursor protein (APP). We set out to determine if Aβ affects primary cilia structure and the Shh signaling cascade.

Methods

We utilized in vitro cell-based assays in combination with fluorescent confocal microscopy to address our study goals. Shh signaling and cilia structure was studied using two different cell lines, mouse NIH3T3 and human HeLa cells. To investigate how Aβ levels affect Shh signaling and cilia structure in these cells, we utilized naturally secreted Aβ as well as synthetic Aβ. Effects on Shh signaling were assessed by luciferase activity while cilia structure was analyzed by fluorescent microscopy.

Results

Here, we report that APP localizes to primary cilia and Aβ treatment results in distorted primary cilia structure. In addition, we demonstrate that Aβ treatment interrupts canonical Shh signal transduction.

Conclusions

Overall, our study illustrates that Aβ can alter primary cilia structure suggesting that elevated Aβ levels, like those observed in AD patients, could have similar effects on neuronal primary cilia in the brain. Additionally, our study suggests that Aβ impairs the Shh signaling pathway. Together our findings shed light on two novel targets for future AD therapeutics.

Primary cilia formation is diminished in schizophrenia and bipolar disorder: A possible marker for these psychiatric diseases

Primary cilium (PC) is a microtubule-rich organelle that protrudes from the plasma membrane and acts as a cellular antenna sensing extracellular signals during brain development. DISC1 (Disrupted-in-Schizophrenia-1) is involved in PC formation and is considered a risk factor for neuropsychiatric disorders. We have previously described altered subcellular distribution of DISC1 and an aberrant microtubule organization in olfactory neuronal precursors (ONP) obtained from schizophrenia (SCZ) and bipolar disorder (BD) patients. Herein, we analyzed in vitro PC formation in healthy control subjects, SCZ and BD patients. The results indicated that 66.73±4.33% of ONP from control subjects showed immunostaining for the PC marker, acetylated α-tubulin. By contrast, only a small percentage of cells in culture from paranoid SCZ and BD patients showed PC staining (SCZ, 12.8±4.43%; BD, 12.32±5.86%). However, cells from an affected proband with disorganized SCZ and a subject with BD displayed a higher percentage of cells with cilia (SCZ, 42.20%; BD, 38.59%). Additionally, cilia elongation was observed in lithium-treated ONP derived from all groups, with a more evident response in cells from the BD group. The present study provides novel evidence that the molecular pathways involved in PC formation are defective in SCZ and BD, and impairment in these processes may be involved in the physiopathology of both diseases. Our observations also suggest that ONP is a patient-derived cell model with a potential use for diagnosis and high-throughput drug screening for brain diseases.

A missense mutation in Katnal1 underlies behavioural, neurological and ciliary anomalies

Microtubule severing enzymes implement a diverse range of tissue-specific molecular functions throughout development and into adulthood. Although microtubule severing is fundamental to many dynamic neural processes, little is known regarding the role of the family member Katanin p60 subunit A-like 1, KATNAL1, in central nervous system (CNS) function. Recent studies reporting that microdeletions incorporating the KATNAL1 locus in humans result in intellectual disability and microcephaly suggest that KATNAL1 may play a prominent role in the CNS; however, such associations lack the functional data required to highlight potential mechanisms which link the gene to disease symptoms. Here we identify and characterise a mouse line carrying a loss of function allele in Katnal1. We show that mutants express behavioural deficits including in circadian rhythms, sleep, anxiety and learning/memory. Furthermore, in the brains of Katnal1 mutant mice we reveal numerous morphological abnormalities and defects in neuronal migration and morphology. Furthermore we demonstrate defects in the motile cilia of the ventricular ependymal cells of mutants, suggesting a role for Katnal1 in the development of ciliary function. We believe the data we present here are the first to associate KATNAL1 with such phenotypes, demonstrating that the protein plays keys roles in a number of processes integral to the development of neuronal function and behaviour.

G-Protein-Coupled Receptor Signaling in Cilia

G-protein-coupled receptors (GPCRs) are the largest and most versatile family of signaling receptors in humans. They respond to diverse external signals, such as photons, proteins, peptides, chemicals, hormones, lipids, and sugars, and mediate a myriad of functions in the human body. Signaling through GPCRs can be optimized by enriching receptors and downstream effectors in discrete cellular domains. Many GPCRs have been found to be selectively targeted to cilia on numerous mammalian cell types. Moreover, investigations into the pathophysiology of human ciliopathies have implicated GPCR ciliary signaling in a number of developmental and cellular pathways. Thus, cilia are now appreciated as an increasingly important nexus for GPCR signaling. Yet, we are just beginning to understand the precise signaling pathways mediated by most ciliary GPCRs and how they impact cellular function and mammalian physiology.

Phencyclidine-induced dysregulation of primary cilia in the rodent brain

Significant roles of the primary cilia in the central nervous system have been reported in neural generation and cognitive functions. However, little is known about the possible pathological changes in brain primary cilia in neuropsychiatric disorders. To obtain an insight into the relationship between cilial dysregulation and schizophrenia, we presently investigated the effects of psychotomimetics, phencyclidine, MK-801 (dizocilpine), and methamphetamine, on morphological and molecular indices in the rodent brain. Using an immunohistochemical technique, we found that a subcutaneous injection of phencyclidine, an NMDA type glutamate receptor (NMDAR) antagonist, caused a reduction in the long axis length of a primary cilium in the CA1 region of the hippocampus without affecting that in the dentate gyrus and medial prefrontal cortex of rats and mice. The region-selective modulation of primary cilia was mimicked by another NMDAR antagonist, MK-801, but not by the indirect dopamine agonist methamphetamine. Furthermore, systemic administration of phencyclidine, but not methamphetamine, down-regulated mRNA expression of primary cilium morphology-related genes, including kif3a, 5-HTR6, RPGRIP1L, and TMEM67, and of genes composing the cilial Wnt/β-catenin signaling pathway, β-catenin, syn2 and Bcl-2, in the hippocampus, but not in the cerebral cortex of rats. These findings suggest that NMDAR hypofunction-induced dysregulation of CA1 primary cilia could be involved in the pathophysiology of dopamine transmission-independent symptoms of schizophrenia.

Using Primary Neurosphere Cultures to Study Primary Cilia

The primary cilium is fundamentally important for the proliferation of neural stem/progenitor cells and for neuronal differentiation during embryonic, postnatal, and adult life. In addition, most differentiated neurons possess primary cilia that house signaling receptors, such as G-protein-coupled receptors, and signaling molecules, such as adenylyl cyclases. The primary cilium determines the activity of multiple developmental pathways, including the sonic hedgehog pathway during embryonic neuronal development, and also functions in promoting compartmentalized subcellular signaling during adult neuronal function. Unsurprisingly, defects in primary cilium biogenesis and function have been linked to developmental anomalies of the brain, central obesity, and learning and memory deficits. Thus, it is imperative to study primary cilium biogenesis and ciliary trafficking in the context of neural stem/progenitor cells and differentiated neurons. However, culturing methods for primary neurons require considerable expertise and are not amenable to freeze-thaw cycles. In this protocol, we discuss culturing methods for mixed populations of neural stem/progenitor cells using primary neurospheres. The neurosphere-based culturing methods provide the combined benefits of studying primary neural stem/progenitor cells: amenability to multiple passages and freeze-thaw cycles, differentiation potential into neurons/glia, and transfectability. Importantly, we determined that neurosphere-derived neural stem/progenitor cells and differentiated neurons are ciliated in culture and localize signaling molecules relevant to ciliary function in these compartments. Utilizing these cultures, we further describe methods to study ciliogenesis and ciliary trafficking in neural stem/progenitor cells and differentiated neurons. These neurosphere-based methods allow us to study cilia-regulated cellular pathways, including G-protein-coupled receptor and sonic hedgehog signaling, in the context of neural stem/progenitor cells and differentiated neurons.

Unique spatiotemporal requirements for intraflagellar transport genes during forebrain development

Primary cilia are organelles extended from virtually all cells and are required for the proper regulation of a number of canonical developmental pathways. The role in cortical development of proteins important for ciliary form and function is a relatively understudied area. Here we have taken a genetic approach to define the role in forebrain development of three intraflagellar transport proteins known to be important for primary cilia function. We have genetically ablated Kif3a, Ift88, and Ttc21b in a series of specific spatiotemporal domains. The resulting phenotypes allow us to draw several conclusions. First, we conclude that the Ttc21b cortical phenotype is not due to the activity of Ttc21b within the brain itself. Secondly, some of the most striking phenotypes are from ablations in the neural crest cells and the adjacent surface ectoderm indicating that cilia transduce critical tissue—tissue interactions in the developing embryonic head. Finally, we note striking differences in phenotypes from ablations only one embryonic day apart, indicating very discrete spatiotemporal requirements for these three genes in cortical development.

Primary cilia as a novel horizon between neuron and environment

The primary cilium, a hair-like sensory organelle found on most mammalian cells, has gained recent attention within the field of neuroscience. Although neural primary cilia have been known to play a role in embryonic central nervous system patterning, we are just beginning to appreciate their importance in the mature organism. After several decades of investigation and controversy, the neural primary cilium is emerging as an important regulator of neuroplasticity in the healthy adult central nervous system. Further, primary cilia have recently been implicated in disease states such as cancer and epilepsy. Intriguingly, while primary cilia are expressed throughout the central nervous system, their structure, receptors, and signaling pathways vary by anatomical region and neural cell type. These differences likely bear relevance to both their homeostatic and neuropathological functions, although much remains to be uncovered. In this review, we provide a brief historical overview of neural primary cilia and highlight several key advances in the field over the past few decades. We then set forth a proposed research agenda to fill in the gaps in our knowledge regarding how the primary cilium functions and malfunctions in nervous tissue, with the ultimate goal of targeting this sensory structure for neural repair following injury.

Neuroanatomical characterization of the cellular and axonal architecture of subcortical band heterotopia in the BXD29-Tlr4lps-2J/J mouse cortex

Subcortical band heterotopia (SBH) are malformations of the human cerebral cortex typically associated with epilepsy and cognitive delay/disability. Rodent models of SBH have demonstrated strong face validity as they are accompanied by both cognitive deficits and spontaneous seizures or reduced seizure threshold. BXD29-Tlr4^lps-2J/J recombinant inbred mice display striking bilateral SBH, partial callosal agenesis, morphological changes in subcortical structures of the auditory pathway, and display sensory deficits in behavioral tests (Rosen et al., 2013; Truong et al., 2013, 2015). Surprisingly, these mice show no cognitive deficits and have a higher seizure threshold to chemi-convulsive treatment (Gabel et al., 2013) making them different than other rodent SBH models described previously. In the present report, we perform a detailed characterization of the cellular and axonal constituents of SBH in BXD29-Tlr4^lps-2J/J mice and demonstrate that various types of interneurons and glia as well as cortical and subcortical projections are found in SBH. In addition, the length of neuronal cilia was reduced in SBH compared to neurons in the overlying and adjacent normotopic cortex. Finally, we describe additional and novel malformations of the hippocampus and neocortex present in BXD29-Tlr4^lps-2J/J mice. Together, our findings in BXD29-Tlr4^lps-2J/J mice are discussed in the context of the known neuroanatomy and phenotype of other SBH rodent models.

Methods for Visualization of Neuronal Cilia

Neuroscientists have been captivated by cilia ever since these slender, microtubule-based projections on the cell body were found to play critical roles in neuronal specification, maintenance, and function. In mammals, the most common cilia marker, acetylated α-tubulin, is extremely difficult to detect in neuronal cilia. Here, we describe methods to detect neuronal cilia in culture, in fixed sections, and in vivo, taking advantage of transgenic mice carrying fluorescently tagged cilia proteins.

The Possible Roles of the Dentate Granule Cell's Leptin and Other Ciliary Receptors in Alzheimer's Neuropathology

Dentate-gyral granule cells in the hippocampus plus dentate gyrus memory-recording/retrieving machine, unlike most other neurons in the brain, are continuously being generated in the adult brain with the important task of separating overlapping patterns of data streaming in from the outside world via the entorhinal cortex. This "adult neurogenesis" is driven by tools in the mature granule cell's cilium. Here we report our discovery of leptin's LepRb receptor in this cilium. In addition, we discuss how ciliary LepRb signaling might be involved with ciliary p75NTR and SSTR3 receptors in adult neurogenesis and memory formation as well as attenuation of Alzheimer's neuropathology by reducing the production of its toxic amyloid-β-derived drivers.